Steering Left - Komatsu 930E-2 Shop Manual

Steering Left

(Refer to Figure 4-7):
When the operator turns the steering wheel "left", the
steering control unit is opened to allow oil coming in
port "P" to pass to the gerotor section of the control
unit to turn the rotor. Oil in the other side of the gerotor
flows through other passages in the control unit valve
and out steering control unit port "L". This oil enters
port "L" of the flow amplifier assembly and goes to a
closed area "B" in the directional valve.
As pressure in this area builds, it also passes into the
spool through orifice "C" to the spring area on the end
of the directional valve. The pressure then moves the
spool compressing the springs on the opposite end.
This movement allows the oil entering area "B" to pass
through the directional valve to area "D" of the amplifier
valve through sleeve "E" holes to a passage between
sleeve "E" and valve "F", through hole "G" in sleeve "E"
where it initially is blocked by the valve body.
As pressure builds up in this area, oil also flows from
area "D", around the outside of sleeve "E", around pin
"H", through orifice "J" to build pressure on the end of
the amplifier valve and opens hole "G" only enough to
allow the flow of oil coming from the steering control
unit to pass to the control area of the directional valve.
At the same time, the movement of sleeve "E" opened
the holes near the spring end to allow the oil from the
priority valve to flow into the center of sleeve "E".
L4-10
This oil now inside sleeve "E" pushes valve "F" against
its spring to give the oil access to a series of holes "K",
that are in the same plane as hole "G". The passage of
oil through holes "K" past the valve body is metered by
holes "K" being opened the same proportion as is hole
"G". The number of holes "K" (7) in sleeve "E" deter-
mine the amount of additional oil that is added to the
steering control unit oil passing through hole "G".
This combined oil going to the center area "Q" of the
directional valve passes out port "CL" of the flow am-
plifier assembly and travels to the steering cylinders to
steer the front wheels to the left. As the cylinders move,
oil is forced to return out the opposite ends, enter port
"CR" of the flow amplifier assembly, pass through the
directional valve to area "M", passes through the return
check valve "N", and exit port "HT" to the hydraulic
reservoir.
At the steering control unit, when the operator turned
the steering wheel, supply oil from port "P" was also
delivered through the control unit valve to port "LS".
This oil enters the flow amplifier assembly through its
"LS" port and builds pressure in the spring area of the
priority valve. This additional force on the spring end of
the priority valve causes area "A" to open and allow the
necessary flow and pressure to pass through the am-
plifier valve to operate the steering cylinders.
The flow amplifier valve includes a relief valve in the
priority valve spring area that is used to control maxi-
mum steering working pressure to 2750 psi (19.0 MPa)
even though supply pressure coming in to port "HP" is
higher. When 2750 psi (19.0 MPa) is obtained, the relief
valve prevents the "LS" pressure from increasing and
thereby allows the priority valve to compress the spring
enough to close off the area "A" when 2750 psi (19.0
MPa) is present.
Steering Circuit L04031